When a vehicle such as a car turns around a bend, the turning force originates from an interaction between the vehicle tires and the road. Since this is very low in height with respect to the centre of gravity of the vehicle, the vehicle may roll around its longitudinal axis. To an extent, such a roll can be absorbed by the vehicle's suspension. However, if the vehicle rolls too far, then one or more of the vehicle's wheels will lose contact with the road.
In extreme situations, this roll, if not addressed by the driver, may lead to a rollover event. Even when the vehicle does not experience a rollover, the rolling motion may still reduce the driver's ability to control the vehicle. Moreover, the sensation of one or more wheels losing contact with the road is disquieting for the driver and any passengers.
Therefore it is typically desirable to avoid situations in which the vehicle experiences significant forces inducing vehicle roll. U.S. Pat. No. 6,065,558 describes a brake system for preventing a friction rollover of a vehicle. The system operates by actuating the brakes of the vehicle in response to a rollover signal indicating that rollover is likely to occur. Braking the vehicle reduces the rolling force, and so helps to prevent rollover. However, the system is dependent on the rollover signal, which is produced by a sensor. U.S. Pat. No. 6,065,558 contemplates using an accelerometer as the sensor, or switches for signaling compression of either of the rebound bumpers. However both of these solutions have drawbacks.
Firstly, if electrical switches in the rebound bumpers are used, then the switches may also be compressed when braking is not required, for example due to an uneven driving surface. This is especially inconvenient in an off-road vehicle.
Secondly, if an accelerometer is used, then the measurements of the accelerometer are subject to contamination due to movements in the vehicle about other axes. In particular, if the vehicle undergoes a pitching motion at the same time as a yawing motion and a rolling motion, then a component of the pitch will be measured as a component of the roll. This will tend to result in false positives causing the vehicle to brake unnecessarily, or worse, false negatives which cause the vehicle to brake too late.
Since the system described in U.S. Pat. No. 6,065,558 is intended to prevent frictional rollover, which is caused when the vehicle is yawing (turning) sharply, this scenario is common.
However, if the pitching motion can be measured accurately, then this information can be used to make a correction to the measurements of the rolling motion. Measuring the pitching motion is not a trivial problem, since sensors which detect the pitching of the vehicle are subject to the same problems with transitory noise as sensors which detect the rolling of the vehicle.
Therefore a system or method for providing vehicle pitch estimation would be desirable.